Embedded systems (e.g., wireless communication devices, wireless data devices, etc.) are in ever growing demand. The types of resources available on embedded systems vary greatly in terms of static and dynamic memory, processing power, display size, battery life, input/output capabilities, etc. Accordingly, there is very little convergence of hardware and software on embedded systems.
As is known to those having ordinary skills in the art, there are many benefits to developing an embedded system using an intermediate language (IL), such as Java, C#, etc., rather than a natively compiled language (e.g., the C programming language). First, porting intermediate language modules to multiple platforms is possible without modifications to the source code unlike with most compiled languages. Second, intermediate languages and their runtime environments often have bug eliminating features such as array bounds checking, automatic garbage collection, and built-in exception-handling, that many compiled languages do not have. Third, intermediate languages typically run quicker than a totally interpreted language.
Realizing the foregoing advantages of intermediate languages, embedded systems are slowly migrating toward intermediate languages operating on runtime environments. As application software derives greater value from runtime environments, it's expected that many future applications will be written using an intermediate language.
One of the most prohibitive factors of using intermediate languages on embedded systems is the speed of execution. While intermediate languages typically operate quicker than interpreted languages, intermediate languages are usually slower than natively compiled languages. For example, intermediate languages such as Java may be up to three or four times slower than natively compiled languages such as C.
One technique for speeding up intermediate language instructions comprises generating native instructions from some of the intermediate language instructions. Typically, only the most frequently used code paths are compiled into native code, and the rest of the code is left as intermediate instructions. While this prior art technique may improve performance, generating native instructions from some of the intermediate language instructions only utilizes a single instruction set of a processor.
Mixed mode processors such as an ARM (previously, the Advanced RISC (Reduced Instruction Set Computer), and prior to that the Acorn RISC Machine, and now simply ARM) compliant processor, have two or more instruction sets such as, for example, a 16-bit instruction set (the Thumb instruction set) and a 32-bit instruction set (the ARM instruction set). Each of these instruction sets has advantages and disadvantages based on how the instruction sets are utilized. For example, the 16-bit Thumb instruction set typically encodes the functionality of the 32-bit ARM instruction in half the number of bits, thereby creating higher code density. An ARM instruction, however, typically has more semantic content than does a Thumb instruction. As is known to those having ordinary skills in the art, this means that an operation implemented with Thumb instructions may require more instructions to perform the equivalent operation implemented with ARM instructions (e.g., 40% more instructions). For example, to use a 16-bit immediate data location, the Thumb instruction set would require two more instructions to move the data into a register than would the ARM instruction set.
Depending on the memory configuration of a system, the ARM code may run significantly faster than the corresponding Thumb code does or vice-versa. For example, it has been estimated that with 32-bit memory, ARM code will run 40% faster than the corresponding Thumb code. However, with 16-bit memory, Thumb code may run 45% faster than the corresponding ARM code. Accordingly, with such large differences in speed and storage characteristics based on individual embedded systems configurations, there is a significant drawback to compiling intermediate language exclusively into one instruction set (e.g., the ARM instruction set). In addition, there is a significant drawback to not compiling all intermediate language instructions into native instructions.